Certain known gas turbine engines include cooling systems configured to direct air from the compressor stage of the engine to the turbine stage of the engine to cool the components in the turbine stage, such as the turbine discs and blades. Since the cooling air is typically bled from the compressor, the work required to compress the cooling air is lost and thus the efficiency of the engine decreases as more cooling air is diverted from the compressor stage to the turbine stage. There is a continuing need to minimize the amount of air diverted from the compressor stage to the turbine stage for cooling.
FIG. 1 is a simplified partial cutaway view of an example gas turbofan engine 10 (sometimes referred to as the “engine” for brevity) having a rotational axis X-X. The engine 10 includes an air intake 11, a propulsive fan 12, an intermediate-pressure compressor 13, a high-pressure compressor 14, a combustor 15, a high-pressure turbine 16, an intermediate-pressure turbine 17, a low-pressure turbine 18, and an exhaust nozzle 19. The high-pressure compressor 14 and the high-pressure turbine 16 are connected via a shaft 20 and rotate together about the rotational axis X-X. The intermediate-pressure compressor 13 and the intermediate-pressure turbine 17 are connected via a shaft 21 and rotate together about the rotational axis X-X. The fan 12 and the low-pressure turbine 18 are connected via a shaft 22 and rotate together about the rotational axis X-X. A fan nacelle 24 generally surrounds the fan 12 and defines the air intake 11 and a bypass duct 23. Fan outlet guide vanes 25 secure the fan nacelle 24 to the core engine casing.
In operation, the fan 12 compresses air entering the air intake 11 to produce a bypass air flow that passes through the bypass duct 23 to provide propulsive thrust and a core air flow into the intermediate-pressure compressor 13. The intermediate-pressure compressor 13 compresses the air before delivering the air to the high-pressure compressor 14. The high-pressure compressor 14 further compresses the air and exhausts the compressed air into the combustor 15. The combustor 15 mixes the compressed air with fuel and ignites the fuel/compressed air mixture. The resultant hot combustion products then expand through—and thereby drive—the high-, intermediate-, and low-pressure turbines 16, 17, and 18 before being exhausted through the exhaust nozzle 19 to provide additional propulsive thrust. The high-, intermediate-, and low-pressure turbines 16, 17, and 18 respectively drive the high-pressure compressor 14, the intermediate-pressure compressor 13, and the fan 12 via the respective shafts 20, 21, and 22.
A conventional cooling system is illustrated in FIGS. 2 and 3. The turbine engine cooling system (sometimes referred to as the “cooling system” for brevity) configured to provide cooling air to regions of the engine 10 to cool those regions. The cooling system is configured to modulate the flow of cooling air to reduce the amount of cooling air flowing to certain regions of the engine 10 during periods in which less cooling is needed.
As shown in FIGS. 2 and 3 a cooling system 100 is fluidly connectable to a cooling air source 92, a control air source 94, and a cooled region 96. The cooled region 96 is any suitable region of the engine 10 to-be-cooled by cooling air from the cooling air source 92. The cooling air source 92 is any suitable source of cooling air, and the control air source 94 is any suitable source of control air. Typically, both the cooling air source and the control air source is one of the compressor stages of the engine 10. The control air source pressure in the example shown in FIGS. 2 and 3 is higher than the cooling air source pressure.
In FIG. 2, the cooled region 96 includes the turbine section cavity in which the turbines stages 16, 17, and 18 may be positioned. The cooling air source 92 may be the intermediate-pressure compressor stage of the engine 10; and the control air source 94 may be the high-pressure compressor stage of the engine 10.
The cooling system 100 includes cooling air supply feeds for delivering the cooling air to the cooled region. Typically, the air supply feeds may be defined by any combination of lines, piping, tubing, ducting or passages defined within the engine casing etc. As illustrated in FIG. 2, the cooling system includes a first supply feed 100a and a second supply feed 100b. The first supply feed 100a as shown is unmodulated and includes segment 102a fed by cooling air source outlet 101.
The second supply feed 100b is configured to be modulated. The second supply feed 100b includes a first segment 102b also feed by outlet 101, a flow control device 110b followed by a second segment 104b. line segment 102a and 102b are in fluid communication via outlet 101, common compressor tap or distribution manifold. FIG. 2 also illustrates the typical components for a modulated supply line including a control air source 94, a control air delivery line 108b and the flow control device 110b. 
The flow control device 110b is a suitable device configured to control whether, and how much cooling air flows from the cooling air source 92 to cooled region 96 via the second supply feed 100b. The flow control device 110b includes a controller 190, a valve 112b and a vortex amplifier 114b. The vortex amplifier 114b has a cooling air inlet, a control air inlet, and a cooling air outlet. The valve 112b has a control air inlet and a control air outlet and is operated by the controller to regulate the amount of control air fed to the vortex amplifier 114b and thus controls the flow of cooling air to the cooled region via the second supply feed 102b. 
The control air delivery line 108b is in fluid communication with the control air source 94 and the vortex amplifier 114b when the valve 112b is opened. The control air source 94 and vortex amplifier 114b are communicatively isolated from one another when the valve 112b is closed.
As shown in FIG. 2, when the second supply feed is not modulated, the flow to the cooled region through the first and second supply feeds are at a design state and represented as arrows 200a and 200b. However, as shown in FIG. 3, when the second supply feed is modulated by opening the valve 112b and restricting cooling air from passing through the vortex amplifier, the flow of cooling air in the non-modulated first supply feed increases as represented by arrow 201a in FIG. 3. This increase in flow through the first supply feed 102a diminishes some of the performance gained through modulation of the second supply feed 102b. Table 1 below illustrates the effects on the first and second supply feeds when the second supply feed is modulated.
TABLE 1Second supply feedSecond supply feedNOT MODULATEDMODULATEDCooling AirCooling AirMass FlowMass FlowRate (lbs/sec)Rate (lbs/sec)First supply feed (102a)0.4890.789Second supply feed (102b)0.3840.016Combined Feed (102a + 102b)0.8730.805
As shown above, the increase in mass flow through the first supply feed significantly offsets the reduction in mass flow in the second supply feed via modulation. In this example a 95 percent reduction in mass flow through the second supply feed only reduces the total mass flow by 10 percent. Thus the potential gain in efficiency via modulation is substantially reduced.